A normal ear transmits sounds as shown in FIG. 1 through the outer ear 101 to the tympanic membrane (eardrum) 102, which moves the ossicles of the middle ear 103 (malleus, incus, and stapes) that vibrate the oval window and round window openings of the cochlea 104. The cochlea 104 is a long narrow organ wound spirally about its axis for approximately two and a half turns. It includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani, which are connected by the cochlear duct. The cochlea 104 forms an upright spiraling cone with a center called the modiolus where the spiral ganglion cells of the acoustic nerve 113 reside. In response to received sounds transmitted by the middle ear 103, the fluid-filled cochlea 104 functions as a transducer to generate electric pulses which are transmitted to the cochlear nerve 113, and ultimately to the brain.
Hearing is impaired when there are problems in the ear's ability to transduce external sounds into meaningful action potentials along the neural substrate of the cochlea 104. To improve impaired hearing, various types of hearing prostheses have been developed. For example, when a hearing impairment is related to the operation of the middle ear 103, a conventional hearing aid or a middle ear implant (MEI) device may be used to provide acoustic-mechanical vibration to the auditory system.
FIG. 1 also shows some components in a typical MEI arrangement where an external audio processor 111 processes ambient sounds to produce an implant communications signal that is transmitted through the skin to an implanted receiver 108. Receiver 108 includes a receiver coil that transcutaneously receives signals, the implant communications signal, which is then demodulated into a transducer stimulation signals which is sent over leads 109 through a surgically created channel in the temporal bone to a floating mass transducer (FMT) 110 secured to the incus bone in the middle ear 103. The transducer stimulation signals cause drive coils within the FMT 110 to generate varying magnetic fields which in turn vibrate a magnetic mass suspended within the FMT 110. The vibration of the inertial mass of the magnet within the FMT 110 creates vibration of the housing of the FMT 110 relative to the magnet. This vibration of the FMT 110 is coupled to the incus in the middle ear 103 and then to the cochlea 104 and is perceived by the user as sound. See U.S. Pat. No. 6,190,305, which is incorporated herein by reference.
Middle ear implants using electromagnetic transducers such as FMT 110 can present some problems. Many are installed using complex surgical procedures which present the usual risks associated with major surgery and which also require disarticulating (disconnecting) one or more of the bones of the middle ear 103. Disarticulation deprives the patient of any residual hearing he or she may have had prior to surgery, placing the patient in a worsened position if the implanted device is later found to be ineffective with improving the patient's hearing. Moreover, fixation of the FMT 110 onto the incus is difficult in many cases with normal middle ear anatomy. During surgery, the short process of the incus ossicle is accessible without the need of complex surgical procedures. Among other things, the incus short process is more oval towards the main body and has a tapering round at the tip of the short process. This makes it difficult to crimp a clip of the FMT 110 onto the short process of the incus and the variations of the incus anatomy in the narrow facial recess. In addition, blood vessels within the incus need to be preserved to avoid necrosis of the incus.
WO2013/009807 from the inventor describes a transducer clamp comprising at the first end of the prosthesis member clamping fingers for securely engaging the outer surface of an enclosed mechanical signal transducer. An ossicle fastener at the second end of the prosthesis member is adapted for secure attachment to one ossicle of a patient middle ear. The ossicle fastener includes parallel planar fastener clips each having a clover shape with springy lobes surrounding an interior region defined by lobe connecting bends. This ossicle fastener is not suitable for coupling to the short process of the incus, because it is too bulky to fit into the middle ear cavity at the respective location and the clover shape with springy lobes cannot couple onto the conical outer surface of the short process of the incus, but slips off.
DE10204780B4 describes an ossicle fastener arrangement comprising two clamps for fixation of a magnet to the malleus ossicle. The clamps are separated from each other so as to fit the anatomy of the malleus and each clamp embraces the thin elongate, more cylindrically-shaped malleus bone. This fixation with conventional clamps is adapted for fixation to the malleus bone and therefore only suitable for fixation to the malleus ossicle. If this fixation were to be used for fixating to the incus, due to its anatomy, this fixation allows for fixating a floating mass transducer between the long and short process of the incus only. This area is surgically difficult to reach and in order for the surgeon to access the fixation location, the surgical procedure that needs to be carried out needs considerable invasive steps and bears the risk of damaging the facial nerve or the tendon on the short process of the incus. In addition, the exerted fixation force onto the incus ossicle for reliable fixation would potentially harm blood vessels within the incus ossicle. This is because the short and long process enclose an angle in between such that the clips of the ossicle fastener would apply opposing traction forces for fixation.
It is an object of the present invention to overcome these shortcomings of the prior art and provide a middle ear implant device and a middle ear coupling member for coupling an implantable mechanical signal transducer to the short process of the incus ossicle in the middle ear of a patient.